If you are able to utilize the whole room and have an empty well I would make a frame out of 2x4 that runs up the walls with the top 2x4 oriented so that the narrow edge is touching the ceiling. Screw vinyl coated hooks into that. You will have to use your imagination a bit to build the frame, but it shouldn't be too difficult. I had a friend who managed to hang four bikes in a space as narrow as 4 or 5 feet in a bachelor pad with similar wooden structure. The less frequently used bikes can have the pedals removed and of course you'l have to hang them opposites so they tuck nice and tight. If you have 10 feet of space you should be able to hang 8 bikes no problem.